Oxidative stress is thought to be a major contributor to the development of retinal degenerative disorders such as macular degeneration, retinopathy of prematurity and diabetic retinopathy. In order to understand the mechanism(s) of oxidative damage to the retina, we have investigated the gene expression in the retina of rats exposed to intense visible light. The expression of heme oxygenase-1 (HO-1), a marker for oxidative stress, in the retina is highly increased following light exposure. The expression of HO-1 mRNA in the retina in response to light was investigated in animals as a function of age (2-12 months). The HO-1 mRNA was analyzed in the retina using Northern blotting and RT-PCR techniques. The HO-1 mRNA was barely detectable when the retina of animals of all age groups were tested prior to the exposure to bright light. However, the light exposure caused a marked increase in the expression of HO-1 mRNA. This response increased with the age of the animal. Also, this response was effectively blocked in animals of all age groups when they were pre-treated with dimethylthiourea, an antioxidant. Thus, it appears that the susceptibility of retina to oxidative damage from light exposure could be increased with an increase in age.